ABDOMINAL CAVITY 401 



last thoracic nerve runs laterally in front of that muscle, close 

 to the lower border of the last rib, and that the ilio-hypogastric 

 and ilio-inguinal nerves cross it obliquely at a lower level. 



M. Quadratus Lumborum. The quadratus lumborum 

 muscle arises from the ilio- lumbar ligament and from the 

 crest of the ilium behind that ligament. It receives two or 

 three slips also from the transverse processes of a correspond- 

 ing number of the lower lumbar vertebrae. As it passes 

 upwards it narrows slightly, and it is inserted into the medial 

 half of the last rib behind the lateral lumbo-costal arch, and 

 by four tendinous slips into the tips of the transverse pro- 

 cesses of the upper four lumbar vertebrae. It is supplied by 

 the anterior rami of the upper four lumbar nerves. It is a 

 lateral flexor of the vertebral column, and acting with its 

 fellow of the opposite side it is a muscle of inspiration, for it 

 helps to fix the lower ribs and so converts them into fixed 

 points from which the diaphragm can act. 



M. Psoas Major. The psoas major muscle has three 

 distinct series of origins from the corresponding side of the 

 vertebral column. It arises: (i) by five fleshy processes 

 from the anterior surfaces and lower borders of the trans- 

 verse processes of the lumbar vertebrae, close to their roots ; 

 (2) by five slips, each of which arises from the intervertebral 

 fibro-cartilage and the contiguous margins of the bodies of 

 two vertebrae the first slip springing from the last thoracic 

 and the first lumbar vertebrae and the intervening fibro- 

 cartilage, and the last slip from the lower two lumbar vertebrae 

 and the intervening fibro-cartilage ; (3) from the tendinous 

 arches which bridge over the lumbar arteries and protect 

 those vessels from the pressure of the contracting muscle. 



The psoas major tapers somewhat as it extends downwards 

 along the brim of the pelvis minor, and a tendon appears on 

 its lateral border, which affords attachment to the fibres of 

 the iliacus. Passing behind the inguinal ligament, it is 

 inserted into the lesser trochanter of the femur. 



It is supplied by the anterior rami of the second, third, 

 and fourth lumbar nerves. 



Another muscle, called the psoas minor, is occasionally present. It 

 springs from the bodies of the last thoracic and first lumbar vertebrae, and 

 the intervertebral fibro-cartilage between them, and, stretching downwards 

 upon the anterior and medial aspect of the psoas major, it ends in a tendon 

 which is inserted into the ilio-pectineal eminence and ilio-pectineal line. 

 VOL. II 26 



